In nonvolatile semiconductor memory devices typified by a NAND flash memory, the increasing of the memory capacity is achieved by the miniaturization of memory cells and the shortening of the pitch of memory cells. However, with the miniaturization and the pitch shortening, the electrical interference between memory cells is becoming significant.
As a method to suppress the interference between memory cells, there is air gap technology. This is a technology in which, when an insulating layer is formed between memory cells, a space is left in the insulating layer. Thereby, the parasitic capacitance between memory cells is reduced to suppress the electrical interference between memory cells.
However, in the insulating layer in which a space is left, a narrow gap of what is called a seam may be formed. If such a seam is formed in the insulating layer, a chemical liquid or an electrode material provided on the upper side of the memory cell may go through the seam to get between memory cells during processes. In such a case, the reliability of the nonvolatile semiconductor memory device is reduced.